1. Field of the Invention
The present invention relates to a vehicle air-conditioning duct and in particular to a vehicle air-conditioning duct with an oblong cross-sectional configuration.
2. Description of the Related Art
An air-conditioning duct for delivering a stream of conditioned air from an air conditioner provided in a console of a vehicle to the rear seats thereof, for example, one for delivering warm air to a foot region of the rear seat area, is often provided in a floor section of the vehicle. The duct is given a laterally oblong cross-sectional shape because of the limited installation space (see FIG. 1). Therefore, when a load is applied vertically onto the duct, for example, when people in the vehicle step on the duct, the duct may be damaged (may collapse or break).
FIGS. 4 and 5 are respectively a plan view and a cross-sectional side view of an air-conditioning duct 40 of the prior art. As shown in FIGS. 4 and 5, a top wall 42 and a bottom wall 44 of the duct 40 are provided with recesses 46 to prevent the duct 40 from being damaged and to increase the structural strength thereof. When these recesses are viewed from the inside of the duct 40, they are seen as projections 48, 50. The projections 48 projecting from the top wall 42 and the projections 50 projecting from the bottom wall 44 contact each other. This further increases the structural strength of the duct 40.
However, the projections 48, 50 projecting into the duct increase the resistance to air flow in the duct 40. More specifically, as shown in FIG. 4, the area of the flow passage for the conditioned air stream flowing from upstream in the direction indicated by the arrow 52 is decreased by the projections 48, 50. After the stream passes the projections 48, 50, the area of the flow passage increases. The decrease and increase of the area of the flow passage increases the flow resistance. Strictly speaking, after the stream is divided into two parts by the projections 48, 50, the divided parts of the stream wrap around to the rear of the projections 48, 50 to join together again. At that time, the stream separates from the projections 48, 50 so that vortexes are generated at the rear of the projections 48, 50. These vortexes increase the flow resistance. Since a plurality of pairs of the projections 48, 50 are formed in the flow direction 52, the stream flowing through the duct 40 encounters them many times and the flow resistance increases each time.
Also, as shown in FIG. 4, the flow passage of the duct 40 usually includes sharp curves. Separation of the stream therefore occurs at the downstream side of an inner curved portion 54 of the duct 40 and the flow resistance increases accordingly.
It is therefore an object of the present invention to provide a vehicle air-conditioning duct that has improved structural strength and minimizes increase in flow resistance to the conditioned air stream.
To achieve the above-mentioned object, the present invention provides a vehicle air-conditioning duct having an oblong cross-sectional configuration that comprises a top wall, a bottom wall and side walls enclosing an interior space, and at least one constriction formed by a projection protruding from at least one of the top wall and the bottom wall into the interior space so as to connect the top wall with the bottom wall, the constriction extending continuously in an air flow direction so that a cross-sectional area of the constriction is constant in the air flow direction.
Although this vehicle air-conditioning duct has an oblong cross-sectional configuration that is weak in vertical structural strength, the structural strength is increased because the duct has the constriction or constrictions extending from the top wall to the bottom wall within the duct so as to connect the top wall with the bottom wall. Since the constriction extends continuously in the direction of air flow through the duct so that the cross-sectional area of the constriction is constant in the air flow direction, flow resistance to the air flowing through the duct ordinarily caused by repeated increase and decrease of the area of the flow passage in the duct can be restricted. That is, since the constriction extends continuously, the flow resistance to the air flowing through the duct that would be caused by vortexes occurring should the constriction extend discontinuously can be eliminated. Consequently, the pressure loss of the conditioned air stream flowing through the duct can be reduced and the flow rate thereof can be increased.
The air-conditioning duct preferably includes a curved portion and the constriction is formed in the curved portion.
In this vehicle air-conditioning duct, since the constriction is formed continuously in the flow direction at the curved portion of the duct, the conditioned air stream flowing over the inner curved portion is guided by the constriction to follow a small radius of curvature so that separation of the stream occurring at the downstream side of the inner curved portion can be restricted. Consequently, the pressure loss of the stream flowing through the duct can be further reduced and the decrease of the flow rate thereof is restricted so that the flow rate is greater than in a prior art air-conditioning duct.
The side walls of the air-conditioning duct are preferably a large-radius side wall and a small-radius side wall in the curved portion, and a distance between the small-radius side wall and the constriction is equal to or smaller than a distance between the large-radius side wall and the constriction.
Also preferably, the side walls of the air-conditioning duct are a large-radius side wall and a small-radius side wall in the curved portion, and two or more of the constrictions are formed spaced apart in a width direction, distances between adjacent pairs of the large-radius side wall, the constrictions and the small-radius side wall being equal or decreasing from the large-radius side wall toward the small-radius side wall.
In the vehicle air-conditioning ducts of these two configurations, the distance between the small-radius side wall and the adjacent constriction is smaller than the distance between the large-radius side wall and the adjacent constriction. This allows the effect of preventing separation of the conditioned air stream flowing on the small-radius side of the curved portion to be enhanced and enables the area of the flow passage of the stream flowing on the large-radius side of the curved portion to be increased so that the pressure loss can be effectively reduced.